The present invention relates generally to display devices, and more particularly to environmentally sensitive display devices encapsulated in barrier stacks to prevent degradation.
There is a need for versatile visual display devices for electronic products of many different types. Many different display devices are presently being used, including liquid crystal displays (LCDs), light emitting diodes (LEDs), light emitting polymers (LEPs), electronic signage using electrophoretic inks, electroluminescent devices (EDs), and phosphorescent devices. Many of these display devices are environmentally sensitive. As used herein, the term environmentally sensitive display device means display devices which are subject to degradation caused by permeation of environmental gases or liquids, such as oxygen and water vapor in the atmosphere or chemicals used in the processing of the electronic product.
Although many current displays use glass substrates, there is a trend toward the use of plastic substrates. Plastic substrates are critical to future generations of electronic products and associated technologies because they are light weight, impact resistant, and cost effective. However, the gas and liquid permeation resistance of plastics is poor, often several orders of magnitude below what is required for sustained device performance. Barrier coatings are applied to substrates to decrease their gas and liquid permeability. Barrier coatings typically consist of single layer thin film inorganic materials, such as Al, SiO2, Al2O3, and Si3N4 vacuum deposited on polymeric substrates. The best single layer coatings reduce oxygen and water vapor permeability to levels of about 0.1 to 1.0 cc/m2/day and about 0.1 to 1.0 g/m2/day, respectively. (Conditions were not reported. The testing is believed to be at 23° C.) However, many displays require oxygen permeability levels of between about 10−6 and 10−5 cc/m2/day, and water vapor permeability levels between about 10−4 and 10−2 g/m2/day. The environmental sensitivity of the display devices limits the lifetime, reliability, and performance of devices constructed on plastics, which has retarded the development of display devices made with plastic substrates.
Thus, there is a need for an improved, lightweight, barrier construction which can be used to encapsulate environmentally sensitive display devices and prevent the deterioration caused by gas and liquid permeation, and for methods for making such encapsulated environmentally sensitive display devices.